Guidewire with an improved flexural rigidity profile

ABSTRACT

Medical devices and methods for making and using the same are disclosed. An example medical device may include a guidewire. The guidewire may include a core wire having a distal portion. A tubular member may be disposed over the distal portion. The tubular member may have a plurality of slots formed therein and may have a longitudinal axis. The tubular member may include a variably spaced slot section that has a flexural rigidity that varies from a first flexural rigidity to a second flexural rigidity. The transition from the first flexural rigidity to the second flexural rigidity may be a function of a fourth power equation. The first flexural rigidity may be in the range of about 1×10 −6  to about 9×10 −5  lbs-inches 2 . The second flexural rigidity may be in the range of about 1×10 −3  to about 5×10 −3  lbs-inches 2 .

CROSS-REFERENCE TO RELATED PUBLICATIONS

This application is a continuation of U.S. application Ser. No.13/077,579, filed Mar. 31, 2011, now U.S. Pat. No. 8,551,021; whichclaims priority under 35 U.S.C. §119 to U.S. Provisional ApplicationSer. No. 61/319,720, filed Mar. 31, 2010, the entire disclosures ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention pertains to medical devices, and methods formanufacturing medical devices. More particularly, the present inventionpertains to elongated medical devices including a slotted tubularmember, components thereof, and methods for manufacturing and using suchdevices.

BACKGROUND

A wide variety of intracorporeal medical devices have been developed formedical use, for example, intravascular use. Some of these devicesinclude guidewires, catheters, and the like. These devices aremanufactured by any one of a variety of different manufacturing methodsand may be used according to any one of a variety of methods. Of theknown medical devices and methods, each has certain advantages anddisadvantages. There is an ongoing need to provide alternative medicaldevices as well as alternative methods for manufacturing and usingmedical devices.

BRIEF SUMMARY

Embodiments of the present disclosure provide design, material,manufacturing method, and use alternatives for medical devices andtubular members for use in medical devices. An example medical devicemay include a guidewire. The guidewire may include a core wire having adistal portion. A tubular member may be disposed over the distalportion. The tubular member may have a plurality of slots formed thereinand may have a longitudinal axis. The tubular member may include avariably spaced slot section that has a flexural rigidity that variesfrom a first flexural rigidity to a second flexural rigidity. Thetransition from the first flexural rigidity to the second flexuralrigidity may be a function of a fourth power equation. The firstflexural rigidity may be in the range of about 1×10⁻⁶ to about 9×10⁻⁵lbs-inches². The second flexural rigidity may be in the range of about1×10⁻³ to about 5×10⁻³ lbs-inches².

Another example guidewire may include a linear-elastic nickel-titaniumcore wire having a distal portion. A super-elastic nickel-titaniumtubular member may be disposed over the distal portion. The tubularmember may have a plurality of slots formed therein and may have alongitudinal axis. The tubular member may include a variably spaced slotsection that has a flexural rigidity that varies from a first flexuralrigidity to a second flexural rigidity. The transition from the firstflexural rigidity to the second flexural rigidity may be a function of afourth power equation. The first flexural rigidity may be in the rangeof about 1×10⁻⁶ to about 9×10⁻⁵ lbs-inches². The second flexuralrigidity may be in the range of about 1×10⁻³ to about 5×10⁻³lbs-inches².

An example method for manufacturing a guidewire may include providing atubular member having a longitudinal axis, forming a first slot in thetubular member at a first position along the longitudinal axis, forminga second slot in the tubular member at a second position along thelongitudinal axis, and forming a plurality of additional slots in thetubular member at a plurality of positions along the longitudinal axis.The first slot, the second slot, and the plurality of additional slotsmay be variably spaced along the longitudinal axis of the tubular memberso as to define a variably spaced slot section that has a flexuralrigidity that varies from a first flexural rigidity to a second flexuralrigidity. The transition from the first flexural rigidity to the secondflexural rigidity may be a function of a fourth power equation. Thefirst flexural rigidity may be in the range of about 1×10⁻⁶ to about9×10⁻⁵ lbs-inches². The second flexural rigidity may be in the range ofabout 1×10⁻³ to about 5×10⁻³ lbs-inches².

The above summary of some embodiments is not intended to describe eachdisclosed embodiment or every implementation of the present disclosure.The Figures, and Detailed Description, which follow, more particularlyexemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The devices and methods of the present disclosure may be more completelyunderstood in consideration of the following detailed description ofvarious embodiments in connection with the accompanying drawings, inwhich:

FIG. 1 is a plan view of an example medical device disposed in a bloodvessel;

FIG. 2 is a partial cross-sectional side view of an example medicaldevice;

FIG. 3 is a partial cross-sectional side view of another example medicaldevice;

FIG. 4 is graph showing the changes in flexural rigidity and changes indiameter of a core wire relative to the distance from the distal end ofthe core wire;

FIG. 5 is graph showing the changes in flexural rigidity in an examplecore wire, an example tubular member, and a guidewire relative to thedistance from the distal end of the example guidewire;

FIG. 6 is a side view of example tubular member;

FIG. 7 is a cross-sectional view of a portion of an example tubularmember;

FIG. 8 is another cross-sectional view of a portion of an exampletubular member; and

FIG. 9 is another cross-sectional view of a portion of an exampletubular member.

While the embodiments described herein are amenable to variousmodifications and alternative forms, specifics thereof have been shownby way of example in the drawings and will be described in detail. Itshould be understood, however, that the intention is not to limit thedevices and methods to the particular embodiments described. On thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the invention.

DETAILED DESCRIPTION

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

All numeric values are herein assumed to be modified by the term“about,” whether or not explicitly indicated. The term “about” generallyrefers to a range of numbers that one of skill in the art would considerequivalent to the recited value (i.e., having the same function orresult). In many instances, the terms “about” may include numbers thatare rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numberswithin that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and5).

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. As used in this specification and theappended claims, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise.

The following detailed description should be read with reference to thedrawings in which similar elements in different drawings are numberedthe same. The drawings, which are not necessarily to scale, depictillustrative embodiments and are not intended to limit the scope of theinvention.

FIG. 1 is a plan view of an example medical device 10, for example aguidewire, disposed in a blood vessel 12. Guidewire 10 may include adistal section 14 that may be generally configured for probing withinthe anatomy of a patient. Guidewire 10 may be used for intravascularprocedures. For example, guidewire 10 may be used in conjunction withanother medical device 16, which may take the form of a catheter, totreat and/or diagnose a medical condition. Of course, numerous otheruses are known amongst clinicians for guidewires, catheters, and othersimilarly configured medical devices.

FIG. 2 is a partial cross-sectional view of guidewire 10. It can be seenthat guidewire 10 may include a core member or core wire 18 and atubular member 20 disposed over at least a portion of core wire 18.Tubular member 20 may have a plurality of slots 30 formed therein. Corewire 18 may include a proximal section 22 and a distal section 24. Aconnector (not shown) may be disposed between and attach proximalsection 22 to distal section 24. Alternatively, core wire 18 may be aunitary member without a connector. A shaping member 26 may be coupledto core wire 18 (for example distal section 24 of core wire 18), tubularmember 20, or both. Shaping member 26 may be made from a relativelyinelastic material so that a clinician can bend or shape the distal endof guidewire 10 into a shape that may facilitate navigation of guidewire10 through the anatomy. Some examples of suitable materials for corewire 18, tubular member 20, shaping member 26, etc. can be found herein.A coil 27, for example a radiopaque coil, may be disposed over core wire18 and shaping member 26. A solder bond 29 may join core wire 18,shaping member 26, and coil 27. Other joining structures and/or methodsare contemplated. A tip member 28 may also be coupled to core wire 18,tubular member 20, or both that may define an atraumatic distal tip ofguidewire 10. In general, tip member 28 may include solder. However,other versions of tip member 28 are contemplated including tip members28 that comprise or form a polymeric tip.

Core wire 18, for example distal section 24 of core wire 18, may includeone or more tapers or tapered sections and a flattened or stamped distalend 25. Core wire 18 may also include one or more constant outerdiameter sections. The tapers or tapered sections may be formed by anumber of different techniques, for example, by centerless grindingmethods, stamping methods, and the like. The centerless grindingtechnique may utilize an indexing system employing sensors (e.g.,optical/reflective, magnetic) to avoid excessive grinding of the corewire 18 section. In addition, the centerless grinding technique mayutilize a CBN or diamond abrasive grinding wheel that is well shaped anddressed to avoid grabbing core wire 18 during the grinding process. Insome embodiments, core wire 18 is centerless ground using a Royal MasterHI-AC centerless grinder to define one or more tapered sections. In someembodiments, core wire 18 is ground using a CNC profile grinder todefine one or more tapered sections.

Although medical device 10 is depicted in FIG. 1 as a guidewire, it isnot intended to be limited to just being a guidewire. Indeed, medicaldevice 10 may take the form of other suitable guiding, diagnosing, ortreating device (including catheters, endoscopic instruments,laparoscopic instruments, etc., and the like) and it may be suitable foruse at other locations and/or body lumens within a patient. For example,FIG. 3 illustrates another example device 110 in the form of a catheter.Catheter 110 may include a generally elongate shaft 131 having aproximal portion 132 and a distal portion 134. A proximal manifold 136may be disposed at proximal portion 132. Manifold 136 may include a hub138 and strain relief 140. A tip member 142 may be disposed at distalportion 134. Tip member 142 may include a radiopaque marker member 144.One or more additional marker members 144 may be disposed along otherportions of catheter 110, for example along distal portion 134 of shaft131. Shaft 131 may include a tubular member 120 that may be similar inform and function to other tubular members disclosed herein includingtubular member 20 illustrated, for example, in FIG. 2. Tubular member120 may have a plurality of slots 130 formed therein. A liner 146 may bedisposed within tubular member 120. Liner 146 may be similar to ananalogous structure disclosed in U.S. Pat. No. 7,001,369 and U.S. PatentApplication Publication No. US 2006/0264904, the entire disclosures ofwhich are herein incorporated by reference. Discussion herein pertainingto tubular member 20 and/or guidewire 10 (e.g., as illustrated in FIG.2) may also be applicable to tubular member 120 and catheter 110, to theextent applicable. Because of their intended use in the vasculature,some medical devices are designed to have particular physicalcharacteristics such as flexibility (e.g., for the purposes of thisdisclosure, flexibility may be also be termed or expressed as bendingstiffness or flexural rigidity). For example, medical devices may bedesigned to be flexible enough in order to bend in a manner sufficientto traverse the tortuous anatomy. At the far distal end of the medicaldevice, it may be desirable to tailor the flexibility of the medicaldevice so that the device can effectively reach its target within thevasculature. For example, in order to reach coronary vessels and/orvessels near the heart, which may have bends, or “take-offs” with anglesof 90° or more, a guidewire may be designed to be quite flexible at thedistal end. However, if the flexibility is too great, the guidewire maynot efficiently turn at these take-offs and, instead, may have atendency to buckle upon itself. Thus, tailoring the flexibility at thedistal end of a guidewire (e.g., within about the first four to sixinches or so of the guidewire) so that it is able to efficiently advancethrough coronary artery take-offs while minimizing the likelihood thatthe guidewire will buckle back upon itself may be desirable.

When designing guidewires, such as polymer tip and/or spring tipguidewires, the core wire may be the major contributor to the overallflexural rigidity of the guidewire. Because the flexural rigidity ofcore wire may be a function of the diameter of the core, it may bedesirable to taper or otherwise size the core wire so that it provides adesired flexural rigidity to the guidewire, for example at the distalend. For example, FIG. 4 is a graph illustrating the flexural rigidityof a core wire and the diameter of the core wire plotted versus thedistance from the distal end of the core wire. The scale on the leftside of the graph is the flexural rigidity in lbs-inch², defined as EIwhere E is Young's modulus of the core wire material (in this example, astainless steel core wire), I is the area moment of inertia (because thecore wire has a round cross-section, the area moment of inertia is πr⁴/4where r is the radius of the core wire). The scale on the right side ofthe graph is the diameter of the core wire in inches. The scale at thebottom of the graph is the distance from the distal end of the core wirein inches.

What can be seen in this graph is that a linear taper or transition indiameter of the core wire results in a non-linear change in flexuralrigidity. Indeed, a linear taper in the core wire may provide a changein flexural rigidity that follows a non-linear transition that may bedefined by a fourth order equation. Stated another way, the change inthe flexural rigidity may be a function of a fourth order polynomial.Such a change in flexural rigidity may be desirable because it mayprovide the core wire with sufficient flexibility to traverse thevasculature and navigate coronary artery take-offs, yet be sufficientlyresistant to buckling.

While coronary guidewires having such core wires may have desirableflexibility characteristics, they may not fully transmit torque from theproximal end to the distal end of the guidewire. This may limit aclinician's ability to accurately navigate the guidewire to its intendeddestination. One way to enhance the torquability in a guidewire may beto include a tubular member about a portion of a core wire such astubular member 20, illustrated in FIG. 2, which may efficiently transmittorque along its length. Because tubular member 20 may include slots 30,it also may be highly flexible. Thus, the combination of a highlyflexible core wire (e.g., core wire 18) and a highly flexible tubularmember (e.g., tubular member 20) may result in a guidewire withdesirable flexibility and torque-transmitting characteristics (e.g.,guidewire 10).

Unlike in polymer tip and spring tip guidewires, where the polymericmaterial and springs coils in the tips may only contribute a negligibleamount to the overall flexural rigidity of the guidewire, the structureof tubular member 20 may be such that it does contribute to the overallflexural rigidity of guidewire 10. Therefore, the flexural rigidity ofcore wire 18 alone may not determine the overall flexural rigidity ofguidewire 10. Because of this, it may be desirable to tailor theflexural rigidity of tubular member 20 so that tubular member 20 canhelp contribute to the flexural rigidity of guidewire 10 in a mannerthat allows guidewire 10 to still efficiently traverse the vasculaturewhile having a tendency to resist buckling.

Tubular member 20 may be fabricated in such a manner that it providesguidewire 10 with desirable flexural rigidity characteristics. Forexample, tubular member 20 may designed so that its flexural rigiditychanges in a non-linear manner. This may include a change in flexuralrigidity that follows a third order to a fifth order equation or, statedanother way, is a function of a third order to a fifth order polynomial(e.g., is based on a mathematical equation that is a third order to afifth order polynomial). For example, the flexural rigidity of thetubular member 20 may follow or otherwise be a function of a fourthorder polynomial. This fourth order transition in flexural rigidity maytake place along the entire length of tubular member 20 or it may occurin one or more sections of tubular member 20. For example, the flexuralrigidity of tubular member 20 may follow a fourth order transitionacross the entire length of tubular member, across about the first fiveinches or so of tubular member 20, or in a section of tubular member 20located along a portion of the first four inches or so of tubular member20.

As indicated above, in some examples, the flexural rigidity of tubularmember 20 may transition according to a fourth power equation orpolynomial. Fourth power equations are a subset of fourth orderequations or polynomials where the lower power coefficients are zero.Thus, a fourth power equation for flexural rigidity may be representedby the following equation:

FR(x)=A+Bx ⁴

where:

FR is the flexural rigidity,

A is the flexural rigidity at the start of the transition,

B is (the flexural rigidity at the end of the transition—the flexuralrigidity at the start of the transition)/(length of the transition)⁴,and

x is the position along the transition and is defined as 0 at the startof the transition.

Thus, the flexural rigidity in tubular member 20 may transition across atransition length from a starting flexural rigidity to an endingflexural rigidity, and this transition may be a function of a fourthpower equation.

FIG. 5 is a graph depicting flexural rigidity (flexural rigidity, FR, inlbs-inch²) for core wire 18, tubular member 20, and guidewire 10. Thescale at the bottom of the graph is the distance from the distal end ofguidewire 10 in inches. Here it can be seen that flexural rigidity ofcore wire 18 changes in a non-linear manner. For example, the flexuralrigidity of core wire 18 may be a function of a fourth order polynomial.Tubular member 20 also has a non-linear change in flexural rigidity andthis change may be a function of a fourth order polynomial (e.g., afourth order polynomial). The overall flexural rigidity of guidewire 10may be essentially the sum of the flexural rigidity of core wire 18 andtubular member 20 and it changes in a non-linear manner (e.g., may be afunction of a fourth order polynomial). Such flexibility characteristicsmay be desirable and may provide guidewire 10 with flexibilitycharacteristics that allow guidewire 10 to traverse the vasculature andnavigate coronary artery take-offs, yet be sufficiently resistant tobuckling.

The structure of tubular member 20 may vary in a number of differentways so as to provide the desired flexural rigidity (e.g., the desiredflexural rigidity along at least a portion of tubular member 20 thatvaries as a function of a fourth power polynomial). FIG. 6 illustratestubular member 20 showing slots 30 formed therein and arranged in apattern that may provide the desired flexural rigidity. For example,tubular member 20 may have a distal uncut or non-slotted section 48disposed at the distal end of tubular member 20. Section 48 may lackslots 30 and may have a length in the range of about 0.01 to 0.1 inches,or about 0.02 to 0.03 inches, or about 0.024 inches.

Next to section 48 may be a distal slotted section 50 where slots 30have an essentially constant spacing. Section 48 may have a length inthe range of about 0.1 to 5 inches, or about 0.1 to 1 inches, or about0.4 to 0.6 inches, or about 0.49 inches. The flexural rigidity ofsection 50 may also be essentially constant. For example, the flexuralrigidity of section 50 may be in the range of about 1×10⁻⁶ to 9×10⁻⁵lbs-inches², or about 5×10⁻⁶ to 3×10⁻⁵ lbs-inches², or about 6×10⁻⁶ to2.1×10⁻⁵ lbs-inches². In one example, the flexural rigidity of section50 may be about 6×10⁻⁶ lbs-inches². In another example, the flexuralrigidity of section may be about 2.1×10⁻⁵ lbs-inches².

Tubular member 20 may also include a mid-distal uncut or non-slottedsection 52. Section 52 may lack slots 30 and may have a length in therange of about 0.001 to 0.1 inches, or about 0.01 to 0.02 inches, orabout 0.012 inches. Tubular member 20 may also include a transitionsection 54 that is disposed adjacent to section 52. The spacing of slots30 in transition section 54 may vary so as to provide section 50 with aflexural rigidity that is a function of a third order to a fifth orderequation (e.g., may be a function of a third order to a fifth orderpolynomial). For example, transition section 54 may have a transition inflexural rigidity that varies as a function of a fourth powerpolynomial. Section 54 may have a length in the range of about 1 to 5inches, or about 1 to 4 inches, or about 1 to 3 inches, or about 2.49inches.

Tubular member 20 may also include a proximal slotted section 56 whereslots 30 have an essentially constant spacing. Section 56 may have alength in the range of about 0.1 to 10 inches, or about 2 to 8 inches,or about 3 to 5 inches, or about 3.95 to 4.25 inches. The flexuralrigidity of section 56 may also be essentially constant. For example,the flexural rigidity of section 56 may be in the range of about 1×10⁻⁴to 9×10⁻³ lbs-inches², or about 1×10⁻³ to 5×10⁻³ lbs-inches², or about1×10⁻³ to 3×10⁻³ lbs-inches², or about 1.42×10⁻³ to 2.64×10⁻³lbs-inches². Next to section 56 may be a proximal uncut section 58,which may lack slots 30 and may have a length in the range of about 0.01to 0.1 inches, or about 0.02 to 0.04 inches, or about 0.03 inches.

It can be appreciated that the above description of tubular member 20 isprovided as an example. Numerous alternative tubular members arecontemplated that may lack one or more of the sections described above,include other sections having similar or different properties, orinclude other structural features.

As indicated above, the flexural rigidity of section 54 may vary. Insome embodiments, the flexural rigidity of section 54 may be a functionof a third to a fifth order polynomial. For example, the flexuralrigidity of section 54 may be a function of a fourth power polynomial[e.g., FR(x)=A+Bx⁴]. In some embodiments, the flexural rigidity ofsection 54 (FR₅₄) may transition from the flexural rigidity of section50 (FR₅₀) to that of section 56 (FR₅₆). For example, the flexuralrigidity of section 54 (FR₅₄) may vary according to the followingequation, where x is the position along the longitudinal axis of tubularmember 20, x_(s) is the distance from the distal end of tubular member20 to the distal end of section 54, x_(f) is the distance from thedistal end of the tubular member 20 to the proximal end of section 54,(x_(f)−x_(s)) is the length of section 54, and where the relativeposition within section 54 is (x−x_(s)):

$\begin{matrix}{{FR}_{54} = {{FR}_{50} + {\left\lbrack {\left( {{FR}_{56} - {FR}_{50}} \right)/\left\{ \left( {x_{f} - x_{s}} \right)^{4} \right\}} \right\rbrack*\left( {x - x_{s}} \right)^{4}}}} \\{= {{FR}_{50} + {\left( {{FR}_{56} - {FR}_{50}} \right)*\left\{ {\left( {x - x_{s}} \right)/\left( {x_{f} - x_{s}} \right)} \right\}^{4}}}}\end{matrix}$

This is just an example. Other equations are contemplated that mayprovide tubular member 20 with the desired flexural rigidity.

Although the above discussion of the flexural rigidity of section 54 isdescribed as being a function of a third order to a fifth orderpolynomial (e.g., a fourth power equation or polynomial), this is notintended to be limiting. For example, the entire length of tubularmember 20 may have a flexural rigidity that varies according to a thirdorder to a fifth order polynomial (e.g., a fourth power equation orpolynomial) or any one or more of the sections of tubular member 20 mayvary in flexural rigidity in this or any other manner.

Forming tubular member 20 with the desired fourth power transition inflexural rigidity along a portion or all of its length may include anumber of procedural steps. For example, these steps may includeproviding or otherwise starting with a tube having a known insidediameter, a known outside diameter, and that is made from a knownmaterial (e.g., having a known Young's modulus). The design may theninclude setting a constant ratio of the beam height to ring width or theselection of a range of beam height to ring width ratios. The term “beamheight” generally refers to the length or width of the beam in theradial direction. The term “ring width” generally refers to the lengthbetween two adjacent slots 30 and an example of ring width, W_(r), isshown in FIG. 6.

The beam height to ring width ratio may be set at a value of about 0.5to 5, or about 1 to 2, or about 1.3 to 1.7, or at a number of individualvalues over these ranges. With these parameters set, sample parts can bemade to establish a “flexural rigidity profile”. For example, one samplepart may be made with essentially “shallow” cuts (e.g., the beam heightmay be relatively high). This sample may represent a “stiff” sample tubeor a tube with a relatively high flexural rigidity. A number of distinctsamples may also be made with shallow cuts, using a number of differentbeam height to ring width ratios. Other sample parts may also be madeincluding a part with essentially “deep” cuts (e.g., the beam height maybe relatively low, which may result in a more flexible tube or a tubewith a relatively low flexural rigidity), again using a number ofdifferent beam height to ring width ratios, and a number of intermediatetubes that fall intermediate (in terms of beam height) between the firsttwo parts may also be made. The intermediate parts may also be made witha number of different beam height to ring width ratios.

The flexural rigidity can then be measured in the sample parts. Usingavailable software (e.g., EXCEL®, available from Microsoft Corporation,Redmond, Wash.; DESIGN EXPERT, available from Stat Ease, Minneapolis,Minn.), the measured flexural rigidities, beam heights, and beam heightto ring width ratios can be entered into a “designed experiment”, whichcan then generate equations that relate flexural rigidity to beamheight, ring width, and beam height to ring width ratio. As analternative to making physical samples, techniques such as mathematicalmodeling (e.g., Finite Element Analysis, etc.) can be used to simulatephysical samples, and theoretical flexural rigidities can be calculated.This information can be entered into a “designed experiment”, as above.If desired, a number of physical samples could be made and measured withrespect to flexural rigidity, to confirm and/or correct the accuracy ofthe mathematical simulation. For the purposes of this disclosure, theequations resulting from the designed experiment will be termed the“mathematical model”.

With the known parameters set (e.g., starting flexural rigidity, endingflexural rigidity, and ratio or range of ratios of beam height to ringwidth), a cut pattern can be established with the desired transition inflexural rigidity (e.g., transitioning as a function of a fourth powerequation). If the beam height to ring width ratio is not constant, themathematical model may include one or more equations that describe thechange in the ratio as a function of distance from a starting point(e.g., the starting point at which a transition in beam height to ringwidth ratio begins). This function may be linear, squared, cubed,polynomial, etc. The mathematical model can be used to determine thebeam height (or cut depth) and ring width needed to achieve a flexuralrigidity at the start of the transition that is equal to the startingflexural rigidity, using the ratio of beam height to ring width definedby the equation noted above. Because the ring width is equal to thedistance between cuts minus the width or kerf of the cutting instrument(e.g., and/or the width of the cut), the distance that the tube istranslated relative to the cutting apparatus can be readily determined.

Next, the fourth power equation can be used to calculate what theflexural rigidity should be at the second cut point. Once this value isknown, the mathematical model can be used to calculate the particularbeam height and ring width that provides the calculated flexuralrigidity. Once a cut is made to define the particular beam height, theprocess can be repeated (e.g., translate the tube the proper distancethat is consistent with the beam height to ring width ratio, calculatethe flexural rigidity at the next cut location using the fourth powerequation, and using the mathematical model to calculate what beam heightwill give the calculated flexural rigidity) until the full length of thetube for which the desired transition spans is cut in the desiredmanner.

FIGS. 7-9 depict a variety of example cross-sectional views takenthrough different portions of tubular member 20 and cuts formed intubular member 20 in order to illustrate some additional variationscontemplated for the distribution or arrangement of slots 30 in tubularmember 20. The description of these figures make use of the words “beam”and/or “beams”. The beams are the portion of tubular member 20, oftenresembling a beam in appearance, that remains after cutting away aportion of tubular member 20 to form slots 30.

Turning now to FIG. 7, when a suitable cutting apparatus cuts intotubular member 20 to form slots 30, the cutting apparatus cuts throughtubular member 20 at a particular angular position (e.g., forconvenience sake assume the angular position is located at the righthand side or the 0° position of tubular member 20) to a position calledthe cut depth CD and defines a slot 60 a (depicted in phantom as theportion of tubular member 20 removed by cutting). In this example, thebeam height BH is the length of width of the beam in the radialdirection. The beam height BH may be related to the cut depth CD and theouter diameter OD of tubular member 20. For example, in at least somecases the “deeper” the cut depth CD, the “shorter” the beam height BH.In fact, the relationship between cut depth CD and beam height BH can berepresented by the equation:

CD=0.5*(OD−BH)

Another cut 60 b may be made in tubular member 20 at the samelongitudinal position (e.g., from the opposite angular position (e.g.,)180°) of tubular member 20 as shown in FIG. 8. Here it can be seen thata pair of beams 62 a/62 b is defined.

Along the length of tubular member 20, additional pairs of slots andbeams can be formed by making additional cuts. In some embodiments, thecuts can be from the same position (e.g., from the 0° and the 180°positions of tubular member 20). Alternatively, the cuts can begin froma different angular position. For example, the first cut made in tubularmember 20 at a subsequent longitudinal position may be rotated a radialdistance or angle A from where the first cut was made at the firstlongitudinal position. Angle A could be a suitable angle such as, forexample, about 60 to 120°, or about 75 to 100°, or about 85°. Anothercut from the opposite side of tubular member 20 defines a second pair ofbeams. At other longitudinal positions, cuts can be rotated to the sameextent or to different extents.

It can be appreciated that the beam pairs (e.g., beam pairs 62 a/62 b)may have centers that align with the tube centerline C (i.e., a linedrawn between the middle of opposing pairs of beams goes through thetube centerline C). While this can be desirable in some embodiments,other arrangements are contemplated that include beam centers that areoffset from the tube centerline C. For example, FIG. 9 depicts a portionof tubular member 20 where beam pairs 64 a/64 b are offset a distance Dfrom the tube centerline C.

In at least some embodiments, one or more sections of tubular member 20may include beam pairs that are offset from the tube centerline C. Forexample, section 50 may include any number of slots 30 (e.g., one, some,or all) that include beams that are offset from the tube centerline C.In some embodiments, all of the slots 30 are offset from the tubecenterline C the same distance. This distance may be about 0.001 to0.007 inches, or about 0.002 to 0.004 inches, or about 0.003 inches. Inother embodiments, the distance that the beams are offset may vary.

Other sections of tubular member 20 may have the same amount of offset(e.g., the distance that the beams are offset from the tube centerline Cis the same), a different amount of offset, or a variable amount ofoffset. For example, in section 54, the offset or distance that thebeams are offset from the tube centerline C at or near the distal end ofsection 54 (e.g., at a first slot which is labeled with reference number66 in FIG. 6) may be the same as the amount of offset in section 50.Over a number of slots or a distance, the amount of offset may graduallyreduce to zero. This transition may occur over a distance of about 0.1to 1 inches, or about 0.2 to 0.5 inches, or about 0.25 inches. Otherdistances are contemplated. Other sections or portions of sections oftubular member 20 may also have offsets that are the same or differentfrom those in sections 50/54, or may have different amounts of offsetaltogether.

The amount of beam offset in section 54 may linearly transition to zerooffset (e.g., beams aligned with the tube centerline C). This lineartransition may be defined by the following relationship:

Offset(x)=0.003*(1−x/0.25)

where:

Offset is the distance from the tube centerline C that the beams areoffset,

x is the distance from the start of section 54.

In addition to variation in offset, other variations are contemplated.For example, the distance between adjacent slots 30 may be termed thering width W_(r) as shown in FIG. 6. A ratio may be established betweenthe beam height BH and the ring width W_(r). In some embodiments, thisratio may be constant in one or more portions of the entire length oftubular member 20. Alternatively, the ratio of the beam height BH andthe ring width W_(r) may vary. For example, the ratio of the beam heightBH and the ring width W_(r) may vary in section 54. This may include anysuitable variation. In some embodiments, the ratio of the beam height BHand the ring width W_(r) may vary such that the ratio at the proximalend of section 54 is greater than at the distal end. Other variationsare contemplated.

In one example, the ratio of the beam height to ring width is constantin section 50 and remains constant over a distal portion of section 54.At a distance of about 0.1 to 3 inches, or about 1 to 3 inches, or about1.95 to 2.25 inches, or about 1.97 to 2.12 inches, the ratio of the beamheight to ring width may begin to vary. For example, the beam height toring width ratio in section 50 may be about 1 to 3, about 1 to 2, about1 to 1.7, about 1.2 to 1.5, or about 1.3. The same may be true of thedistal portion of section 54. The beam height to ring width ratio maythen vary over a length of section 54. The transition may be a lineartransition (e.g., the beam height to ring width ratio increaseslinearly) over a length of about 0.1 to 1 inches, about 0.25 to 1inches, about 0.3 to 0.6 inches, about 0.38 to 0.53 inches, or otherwisea distance sufficient to extend to the proximal end of section 54. Thebeam height to ring width ratio at the end of the transition may beabout 1 to 2, about 1.3 to 1.8, or about 1.6 to 1.7.

Various embodiments of arrangements and configurations of slots 30 arecontemplated that may be used in addition to what is described above ormay be used in alternate embodiments. For example, in some embodiments,at least some, if not all of slots 30 are disposed at the same or asimilar angle with respect to the longitudinal axis of tubular member20. As shown, slots 30 can be disposed at an angle that isperpendicular, or substantially perpendicular, and/or can becharacterized as being disposed in a plane that is normal to thelongitudinal axis of tubular member 20. However, in other embodiments,slots 30 can be disposed at an angle that is not perpendicular, and/orcan be characterized as being disposed in a plane that is not normal tothe longitudinal axis of tubular member 20. Additionally, a group of oneor more slots 30 may be disposed at different angles relative to anothergroup of one or more slots 30. The distribution and/or configuration ofslots 30 can also include, to the extent applicable, any of thosedisclosed in U.S. Pat. Publication No. US 2004/0181174, the entiredisclosure of which is herein incorporated by reference.

Slots 30 may be provided to enhance the flexibility of tubular member 20while still allowing for suitable torque transmission characteristics.Slots 30 may be formed such that one or more rings and/or tube segmentsinterconnected by one or more segments and/or beams that are formed intubular member 20, and such tube segments and beams may include portionsof tubular member 20 that remain after slots 30 are formed in the bodyof tubular member 20. Such an interconnected structure may act tomaintain a relatively high degree of torsional stiffness, whilemaintaining a desired level of lateral flexibility. In some embodiments,some adjacent slots 30 can be formed such that they include portionsthat overlap with each other about the circumference of tubular member20. In other embodiments, some adjacent slots 30 can be disposed suchthat they do not necessarily overlap with each other, but are disposedin a pattern that provides the desired degree of lateral flexibility.

Additionally, slots 30 can be arranged along the length of, or about thecircumference of, tubular member 20 to achieve desired properties. Forexample, adjacent slots 30, or groups of slots 30, can be arranged in asymmetrical pattern, such as being disposed essentially equally onopposite sides about the circumference of tubular member 20, or can berotated by an angle relative to each other about the axis of tubularmember 20. Additionally, adjacent slots 30, or groups of slots 30, maybe equally spaced along the length of tubular member 20, or can bearranged in an increasing or decreasing density pattern, or can bearranged in a non-symmetric or irregular pattern. Other characteristics,such as slot size, slot shape, and/or slot angle with respect to thelongitudinal axis of tubular member 20, can also be varied along thelength of tubular member 20 in order to vary the flexibility or otherproperties. In other embodiments, moreover, it is contemplated that theportions of the tubular member, such as a proximal section, or a distalsection, or the entire tubular member 20, may not include any such slots30.

As suggested herein, slots 30 may be formed in groups of two, three,four, five, or more slots 30, which may be located at substantially thesame location along the axis of tubular member 20. Alternatively, asingle slot 30 may be disposed at some or all of these locations. Withinthe groups of slots 30, there may be included slots 30 that are equal insize (i.e., span the same circumferential distance around tubular member20). In some of these as well as other embodiments, at least some slots30 in a group are unequal in size (i.e., span a differentcircumferential distance around tubular member 20). Longitudinallyadjacent groups of slots 30 may have the same or differentconfigurations. For example, some embodiments of tubular member 20include slots 30 that are equal in size in a first group and thenunequally sized in an adjacent group. It can be appreciated that ingroups that have two slots 30 that are equal in size and aresymmetrically disposed around the tube circumference, the centroid ofthe pair of beams (i.e., the portion of tubular member 20 remainingafter slots 30 are formed therein) is coincident with the central axisof tubular member 20. Conversely, in groups that have two slots 30 thatare unequal in size and whose centroids are directly opposed on the tubecircumference, the centroid of the pair of beams can be offset from thecentral axis of tubular member 20. Some embodiments of tubular member 20include only slot groups with centroids that are coincident with thecentral axis of the tubular member 20, only slot groups with centroidsthat are offset from the central axis of tubular member 20, or slotgroups with centroids that are coincident with the central axis oftubular member 20 in a first group and offset from the central axis oftubular member 20 in another group. The amount of offset may varydepending on the depth (or length) of slots 30 and can include othersuitable distances.

Slots 30 can be formed by methods such as micro-machining, saw-cutting(e.g., using a diamond grit embedded semiconductor dicing blade),electron discharge machining, grinding, milling, casting, molding,chemically etching or treating, or other known methods, and the like. Insome such embodiments, the structure of the tubular member 20 is formedby cutting and/or removing portions of the tube to form slots 30. Someexample embodiments of appropriate micromachining methods and othercutting methods, and structures for tubular members including slots andmedical devices including tubular members are disclosed in U.S. Pat.Publication Nos. 2003/0069522 and 2004/0181174-A2; and U.S. Pat. Nos.6,766,720; and 6,579,246, the entire disclosures of which are hereinincorporated by reference. Some example embodiments of etching processesare described in U.S. Pat. No. 5,106,455, the entire disclosure of whichis herein incorporated by reference. It should be noted that the methodsfor manufacturing guidewire 10 may include forming slots 30 in tubularmember 20 using these or other manufacturing steps.

In at least some embodiments, slots 30 may be formed in tubular memberusing a laser cutting process. The laser cutting process may include asuitable laser and/or laser cutting apparatus. For example, the lasercutting process may utilize a fiber laser. Utilizing processes likelaser cutting may be desirable for a number of reasons. For example,laser cutting processes may allow tubular member 20 to be cut into anumber of different cutting patterns in a precisely controlled manner.This may include variations in the slot width, ring width, beam heightand/or width, etc. Furthermore, changes to the cutting pattern can bemade without the need to replace the cutting instrument (e.g., blade).This may also allow smaller tubes (e.g., having a smaller outerdiameter) to be used to form tubular member 20 without being limited bya minimum cutting blade size. Consequently, tubular members 20 may befabricated for use in neurological devices or other devices where arelatively small size may be desired.

The materials that can be used for the various components of guidewire10 (and/or other guidewires disclosed herein) and the various tubularmembers disclosed herein may include those commonly associated withmedical devices. For simplicity purposes, the following discussion makesreference to tubular member 20 and other components of guidewire 10.However, this is not intended to limit the devices and methods describedherein, as the discussion may be applied to other similar tubularmembers and/or components of tubular members or devices disclosedherein.

Tubular member 20 and/or other components of guidewire 10 may be madefrom a metal, metal alloy, polymer (some examples of which are disclosedbelow), a metal-polymer composite, ceramics, combinations thereof, andthe like, or other suitable material. Some examples of suitable metalsand metal alloys include stainless steel, such as 304V, 304L, and 316LVstainless steel; mild steel; nickel-titanium alloy such aslinear-elastic and/or super-elastic nitinol; other nickel alloys such asnickel-chromium-molybdenum alloys (e.g., UNS: N06625 such as INCONEL°625, UNS: N06022 such as HASTELLOY® C-22®, UNS: N10276 such asHASTELLOY® C276®, other HASTELLOY® alloys, and the like), nickel-copperalloys (e.g., UNS: N04400 such as MONEL® 400, NICKELVAC® 400, NICORROS®400, and the like), nickel-cobalt-chromium-molybdenum alloys (e.g., UNS:R30035 such as MP35-N® and the like), nickel-molybdenum alloys (e.g.,UNS: N10665 such as HASTELLOY® ALLOY B2®), other nickel-chromium alloys,other nickel-molybdenum alloys, other nickel-cobalt alloys, othernickel-iron alloys, other nickel-copper alloys, other nickel-tungsten ortungsten alloys, and the like; cobalt-chromium alloys;cobalt-chromium-molybdenum alloys (e.g., UNS: R30003 such as ELGILOY®,PHYNOX®, and the like); platinum enriched stainless steel; titanium;combinations thereof; and the like; or any other suitable material.

As alluded to herein, within the family of commercially availablenickel-titanium or nitinol alloys, is a category designated “linearelastic” or “non-super-elastic” which, although may be similar inchemistry to conventional shape memory and super elastic varieties, mayexhibit distinct and useful mechanical properties. Linear elastic and/ornon-super-elastic nitinol may be distinguished from super elasticnitinol in that the linear elastic and/or non-super-elastic nitinol doesnot display a substantial “superelastic plateau” or “flag region” in itsstress/strain curve like super elastic nitinol does. Instead, in thelinear elastic and/or non-super-elastic nitinol, as recoverable strainincreases, the stress continues to increase in a substantially linear,or a somewhat, but not necessarily entirely linear relationship untilplastic deformation begins or at least in a relationship that is morelinear that the super elastic plateau and/or flag region that may beseen with super elastic nitinol. Thus, for the purposes of thisdisclosure linear elastic and/or non-super-elastic nitinol may also betermed “substantially” linear elastic and/or non-super-elastic nitinol.

In some cases, linear elastic and/or non-super-elastic nitinol may alsobe distinguishable from super elastic nitinol in that linear elasticand/or non-super-elastic nitinol may accept up to about 2-5% strainwhile remaining substantially elastic (e.g., before plasticallydeforming) whereas super elastic nitinol may accept up to about 8%strain before plastically deforming. Both of these materials can bedistinguished from other linear elastic materials such as stainlesssteel (that can also can be distinguished based on its composition),which may accept only about 0.2 to 0.44 percent strain beforeplastically deforming.

In some embodiments, the linear elastic and/or non-super-elasticnickel-titanium alloy is an alloy that does not show anymartensite/austenite phase changes that are detectable by differentialscanning calorimetry (DSC) and dynamic metal thermal analysis (DMTA)analysis over a large temperature range. For example, in someembodiments, there may be no martensite/austenite phase changesdetectable by DSC and DMTA analysis in the range of about −60 degreesCelsius (° C.) to about 120° C. in the linear elastic and/ornon-super-elastic nickel-titanium alloy. The mechanical bendingproperties of such material may therefore be generally inert to theeffect of temperature over this very broad range of temperature. In someembodiments, the mechanical bending properties of the linear elasticand/or non-super-elastic nickel-titanium alloy at ambient or roomtemperature are substantially the same as the mechanical properties atbody temperature, for example, in that they do not display asuper-elastic plateau and/or flag region. In other words, across a broadtemperature range, the linear elastic and/or non-super-elasticnickel-titanium alloy maintains its linear elastic and/ornon-super-elastic characteristics and/or properties.

In some embodiments, the linear elastic and/or non-super-elasticnickel-titanium alloy may be in the range of about 50 to about 60 weightpercent nickel, with the remainder being essentially titanium. In someembodiments, the composition is in the range of about 54 to about 57weight percent nickel. One example of a suitable nickel-titanium alloyis FHP-NT alloy commercially available from Furukawa Techno Material Co.of Kanagawa, Japan. Some examples of nickel titanium alloys aredisclosed in U.S. Pat. Nos. 5,238,004 and 6,508,803, which areincorporated herein by reference. Other suitable materials may includeULTANIUM™ (available from Neo-Metrics) and GUM METAL™ (available fromToyota). In some other embodiments, a superelastic alloy, for example asuperelastic nitinol can be used to achieve desired properties.

In at least some embodiments, portions or all of core wire 18 and/ortubular member 20 may also be doped with, made of, or otherwise includea radiopaque material. Radiopaque materials are understood to bematerials capable of producing a relatively bright image on afluoroscopy screen or another imaging technique during a medicalprocedure. This relatively bright image aids the user of guidewire 10 indetermining its location. Some examples of radiopaque materials caninclude, but are not limited to, gold, platinum, palladium, tantalum,tungsten alloy, polymer material loaded with a radiopaque filler, andthe like. Additionally, other radiopaque marker bands and/or coils mayalso be incorporated into the design of guidewire 10 to achieve the sameresult.

In some embodiments, a degree of Magnetic Resonance Imaging (MRI)compatibility is imparted into guidewire 10. For example, to enhancecompatibility with MRI machines, it may be desirable to make core wire18 and/or tubular member 20, or other portions of the guidewire 10, in amanner that would impart a degree of MRI compatibility. For example,core wire 18 and/or tubular member 20, or portions thereof, may be madeof a material that does not substantially distort the image and createsubstantial artifacts (i.e., gaps in the image). Certain ferromagneticmaterials, for example, may not be suitable because they may createartifacts in an MRI image. Core wire 18 and/or tubular member 20, orportions thereof, may also be made from a material that the MRI machinecan image. Some materials that exhibit these characteristics include,for example, tungsten, cobalt-chromium-molybdenum alloys (e.g., UNS:R30003 such as ELGILOY®, PHYNOX®, and the like),nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such asMP35-N® and the like), nitinol, and the like, and others.

Referring now to core wire 18, the entire core wire 18 can be made ofthe same material along its length, or in some embodiments, can includeportions or sections made of different materials. In some embodiments,the material used to construct core wire 18 is chosen to impart varyingflexibility and stiffness characteristics to different portions of corewire 18. For example, proximal section 22 and distal section 24 of corewire 18 may be formed of different materials, for example, materialshaving different moduli of elasticity, resulting in a difference inflexibility. In some embodiments, the material used to constructproximal section 22 can be relatively stiff for pushability andtorqueability, and the material used to construct distal section 24 canbe relatively flexible by comparison for better lateral trackability andsteerability. For example, proximal section 22 can be formed ofstraightened 304v stainless steel wire or ribbon and distal section 24can be formed of a straightened super elastic or linear elastic alloy,for example a nickel-titanium alloy wire or ribbon.

In embodiments where different portions of core wire 18 are made ofdifferent materials, the different portions can be connected using asuitable connecting technique and/or with a connector. For example, thedifferent portions of core wire 18 can be connected using welding(including laser welding), soldering, brazing, adhesive, or the like, orcombinations thereof. These techniques can be utilized regardless ofwhether or not a connector is utilized. The connector may include astructure generally suitable for connecting portions of a guidewire. Oneexample of a suitable structure includes a structure such as a hypotubeor a coiled wire which has an inside diameter sized appropriately toreceive and connect to the ends of the proximal portion and the distalportion. Other suitable configurations and/or structures can be utilizedfor connector 26 including those connectors described in U.S. Pat. Nos.6,918,882 and 7,071,197 and/or in U.S. Patent Pub. No. 2006-0122537, theentire disclosures of which are herein incorporated by reference.

A sheath or covering (not shown) may be disposed over portions or all ofcore wire 18 and/or tubular member 20 that may define a generally smoothouter surface for guidewire 10. In other embodiments, however, such asheath or covering may be absent from a portion of all of guidewire 10,such that tubular member 20 and/or core wire 18 may form the outersurface. The sheath may be made from a polymer or other suitablematerial. Some examples of suitable polymers may includepolytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE),fluorinated ethylene propylene (FEP), polyoxymethylene (POM, forexample, DELRIN® available from DuPont), polyether block ester,polyurethane (for example, Polyurethane 85A), polypropylene (PP),polyvinylchloride (PVC), polyether-ester (for example, ARNITEL®available from DSM Engineering Plastics), ether or ester basedcopolymers (for example, butylene/poly(alkylene ether) phthalate and/orother polyester elastomers such as HYTREL® available from DuPont),polyamide (for example, DURETHAN® available from Bayer or CRISTAMID®available from Elf Atochem), elastomeric polyamides, blockpolyamide/ethers, polyether block amide (PEBA, for example availableunder the trade name PEBAX®), ethylene vinyl acetate copolymers (EVA),silicones, polyethylene (PE), Marlex high-density polyethylene, Marlexlow-density polyethylene, linear low density polyethylene (for exampleREXELL®), polyester, polybutylene terephthalate (PBT), polyethyleneterephthalate (PET), polytrimethylene terephthalate, polyethylenenaphthalate (PEN), polyetheretherketone (PEEK), polyimide (PI),polyetherimide (PEI), polyphenylene sulfide (PPS), polyphenylene oxide(PPO), poly paraphenylene terephthalamide (for example, KEVLAR®),polysulfone, nylon, nylon-12 (such as GRILAMID® available from EMSAmerican Grilon), perfluoro(propyl vinyl ether) (PFA), ethylene vinylalcohol, polyolefin, polystyrene, epoxy, polyvinylidene chloride (PVdC),poly(styrene-b-isobutylene-b-styrene) (for example, SIBS and/or SIBS50A), polycarbonates, ionomers, biocompatible polymers, other suitablematerials, or mixtures, combinations, copolymers thereof, polymer/metalcomposites, and the like. In some embodiments the sheath can be blendedwith a liquid crystal polymer (LCP). For example, the mixture cancontain up to about 6 percent LCP.

In some embodiments, the exterior surface of the guidewire 10(including, for example, the exterior surface of core wire 18 and/or theexterior surface of tubular member 20) may be sandblasted, beadblasted,sodium bicarbonate-blasted, electropolished, etc. In these as well as insome other embodiments, a coating, for example a lubricious, ahydrophilic, a protective, or other type of coating may be applied overportions or all of the sheath, or in embodiments without a sheath overportion of core wire 18 and/or tubular member, or other portions ofdevice 10. Alternatively, the sheath may comprise a lubricious,hydrophilic, protective, or other type of coating. Hydrophobic coatingssuch as fluoropolymers provide a dry lubricity which improves guidewirehandling and device exchanges. Lubricious coatings improve steerabilityand improve lesion crossing capability. Suitable lubricious polymers arewell known in the art and may include silicone and the like, hydrophilicpolymers such as high-density polyethylene (HDPE),polytetrafluoroethylene (PTFE), polyarylene oxides,polyvinylpyrolidones, polyvinylalcohols, hydroxy alkyl cellulosics,algins, saccharides, caprolactones, and the like, and mixtures andcombinations thereof. Hydrophilic polymers may be blended amongthemselves or with formulated amounts of water insoluble compounds(including some polymers) to yield coatings with suitable lubricity,bonding, and solubility. Some other examples of such coatings andmaterials and methods used to create such coatings can be found in U.S.Pat. Nos. 6,139,510 and 5,772,609, which are incorporated herein byreference.

The coating and/or sheath may be formed, for example, by coating,extrusion, co-extrusion, interrupted layer co-extrusion (ILC), or fusingseveral segments end-to-end. The same may be true of tip member 28. Thelayer may have a uniform stiffness or a gradual reduction in stiffnessfrom the proximal end to the distal end thereof. The gradual reductionin stiffness may be continuous as by ILC or may be stepped as by fusingtogether separate extruded tubular segments. The outer layer may beimpregnated with a radiopaque filler material to facilitate radiographicvisualization. Those skilled in the art will recognize that thesematerials can vary widely without deviating from the scope of thepresent invention.

The disclosures of U.S. Patent Application Publication Nos. US2009/0118675, US 2009/0254000, and US 2009/0177185, the entiredisclosures of which are herein incorporated by reference, may pertainto this disclosure. The disclosure of U.S. Pat. No. 6,106,488, theentire disclosure of which is herein incorporated by reference, may alsopertain to this disclosure.

It should be understood that this disclosure is, in many respects, onlyillustrative. Changes may be made in details, particularly in matters ofshape, size, and arrangement of steps without exceeding the scope of theinvention. The invention's scope is, of course, defined in the languagein which the appended claims are expressed.

What is claimed is:
 1. A catheter, comprising: a tubular member having alongitudinal axis and having a lumen defined therein; wherein thetubular member has a plurality of slots formed therein; wherein thetubular member includes a variably spaced slot section that has aflexural rigidity that varies from a first flexural rigidity to a secondflexural rigidity, and wherein the transition from the first flexuralrigidity to the second flexural rigidity is a function of a fourth orderequation; wherein the first flexural rigidity is in the range of about1×10⁻⁶ to about 9×10⁻⁵ lbs-inches²; and wherein the second flexuralrigidity is in the range of about 1×10⁻³ to about 5×10⁻³ lbs-inches². 2.The catheter of claim 1, wherein the second flexural rigidity is in therange of about 1×10⁻³ to about 3×10⁻³ lbs-inches².
 3. The catheter ofclaim 1, wherein the second flexural rigidity is in the range of about1.42×10⁻³ to about 2.64×10⁻³ lbs-inches².
 4. The catheter of claim 1,wherein the tubular member has a distal end and wherein the tubularmember includes a first non-slotted section disposed at the distal end,the first non-slotted section being free of slots.
 5. The catheter ofclaim 4, wherein the tubular member includes a first constantly spacedslot section that includes slots that have a constant spacing along thelongitudinal axis, the first constantly spaced slot section beingdisposed adjacent to the first non-slotted section.
 6. The catheter ofclaim 5, wherein the tubular member includes a second constantly spacedslot section that includes slots that have a constant spacing along thelongitudinal axis.
 7. The catheter of claim 6, wherein the variablyspaced slot section is disposed between the first constantly spaced slotsection and the second constantly spaced slot section.
 8. The catheterof claim 7, wherein the tubular member includes a second non-slottedsection disposed between the first constantly spaced slot section andthe variably spaced slot section, the second non-slotted section beingfree of slots.
 9. The catheter of claim 8, wherein the tubular memberhas a proximal end and wherein the tubular member includes a thirdnon-slotted section disposed at the proximal end, the third non-slottedsection being free of slots.
 10. The catheter of claim 1, wherein theslots define a beam height for a pair of beams at a longitudinalposition along the tubular member, wherein a distance between twolongitudinally adjacent slots defines a ring width, and wherein theratio of the beam height to ring width is constant along at least aportion of the tubular member.
 11. The catheter of claim 10, wherein theratio of beam height to ring width is constant in a first portion of thetubular member and wherein the ratio of beam height to ring width variesin a second portion of the tubular member.
 12. The catheter of claim 11,wherein the ratio of beam height to ring width varies along the variablyspaced slot section.
 13. The catheter of claim 1, wherein the slotsdefine beams in the tubular member and wherein at least some of thebeams are offset from a centerline of the tubular member.
 14. Thecatheter of claim 13, wherein the beams are aligned with the centerlinealong a portion of the tubular member and wherein the beams are offsetfrom the centerline along a second portion of the tubular member. 15.The catheter of claim 14, wherein the variably spaced slot sectionincludes beams that are offset a distance from the centerline of thetubular member.
 16. The catheter of claim 15, wherein the variablespaced slot section includes a transition where the beams that areoffset from the centerline transition from being offset by the distanceto the beams that are aligned with the centerline of the tubular member.17. A catheter, comprising: a super-elastic nickel-titanium tubularmember having a longitudinal axis and having a lumen defined therein;wherein the tubular member has a plurality of slots formed therein;wherein the tubular member includes a variably spaced slot section thathas a flexural rigidity that varies from a first flexural rigidity to asecond flexural rigidity, and wherein the transition from the firstflexural rigidity to the second flexural rigidity is a function of afourth order equation; wherein the first flexural rigidity is in therange of about 1×10⁻⁶ to about 9×10⁻⁵ lbs-inches²; and wherein thesecond flexural rigidity is in the range of about 1×10⁻³ to about 5×10⁻³lbs-inches².
 18. The catheter of claim 17, wherein the tubular memberincludes a first constantly spaced slot section and a second constantlyspaced slot section that each include slots that are spaced a constantdistance along the longitudinal axis.
 19. The catheter of claim 18,wherein the variably spaced slot section is disposed between the firstconstantly spaced slot section and the second constantly spaced slotsection.
 20. A method for manufacturing a catheter, comprising: forminga first slot in a tubular member at a first position along alongitudinal axis of the tubular member; forming a second slot in thetubular member at a second position along the longitudinal axis; forminga plurality of additional slots in the tubular member at a plurality ofpositions along the longitudinal axis; and wherein the first slot, thesecond slot, and the plurality of additional slots are variably spacedalong the longitudinal axis so as to define a variably spaced slotsection wherein the tubular member includes a variably spaced slotsection that has a flexural rigidity that varies from a first flexuralrigidity to a second flexural rigidity, wherein the transition from thefirst flexural rigidity to the second flexural rigidity is a function ofa fourth order equation, wherein the first flexural rigidity is in therange of about 1×10⁻⁶ to about 9×10⁻⁵ lbs-inches², and wherein thesecond flexural rigidity is in the range of about 1×10⁻³ to about 5×10⁻³lbs-inches².